The central theme of HL54131 is to study genes of importance in vascular diseases. Work carried out during the previous grant cycle focused on survivin as a hi-functional inhibitor of apoptosis and mitotic regulator in angiogenic endothelium. Three new paradigms emerged from these experiments that constitute the foundation of the present continuation application. First, survivin was identified as a mediator of PDGF-dependent survival in smooth muscle cells, and molecular interference with the survivin pathway prevented pathologic vascular remodeling after acute arterial injury, in vivo. Second, the mechanism of apoptosis inhibition by survivin was linked to the upstream initiation of mitochondrial cell death, and a discrete pool ot survivin was shown to localize to mitochondria. Third, survivin was characterized as a novel cytoprotective factor induced by Wnt/TCF/beta-catenin, a gene patterning pathway that preserves the pluripotency of tissue stem cells and bone marrow progenitors. Therefore, a unifying hypothesis that survivin maintains the homeostasis of smooth muscle cells and their progenitors during vascular injury can be formulated, and will be investigated in the present continuation application. In the first specific aim, experiments will map the structural and signaling requirements of PDGF induction of survivin in smooth muscle cells. This is a growth factor-specific pathway and will be characterized with respect to Wnt/TCF/beta-catenin gene expression, modulation of cyclin-dependent kinase inhibitors, ERK signaling, activation of PI3 kinase/Akt, and STAT phosphorylation. The second specific aim will dissect the role of mitochondrial survivin in apoptosis inhibition, addressing mechanisms of mitochondrial trafficking, permeability transition, apoptosome assembly, and enhanced lAP-dependent cytoprotection. The third specific aim will determine the importance of survivin in cell viability, proliferation, and colony formation of bone marrow and smooth muscle cell progenitors. The impact of this pathway in pathologic vascular remodeling after acute arterial injury will be determined in bone marrow transplantation experiments using transgenic or retroviral manipulation of survivin expression/function in progenitor cells. Overall, the experimental plan is designed to elucidate a novel survival pathway central to smooth muscle cell homeostasis during acute vascular injury.